This invention relates to an improved arrangement for securing armature bars in radially oriented slots in a stator core body.
In large generators, armature bars typically comprise many copper strands wrapped with many layers of insulating tape and conducting armor, to thus provide a rigid, solid member with a hard outer surface. In certain stator designs, two such armature bars are secured in each of several radial slots in the stator core body, stacked one above the other, with fillers, top ripple springs to restrain the bars radially, and side ripple springs to increase friction between the bar and the slot side wall. The bars are held in place by wedges driven into longitudinal dovetail grooves formed near the top of each slot, along opposite side walls of the slot.
To accommodate the side ripple springs, ample slot side clearance is provided, but the result is undesirable dead air space between the bars and the slot walls.
In U.S. Pat. No. 5,708,315, a stretchable coil wrapper is disclosed for covering an armature on three sides with an elastomeric sheet. After the bar is covered on three sides (i.e., in a U-shape), the elastomer is stretched by a coil stretching device, thinning the elastomer and permitting the bar to be inserted into the radial slot. Then, after the bar is inserted into the slot, the device is removed so that the elastomer contracts, filling the spaces between the bar and the slot walls. Excess material is then trimmed to fit.
In this invention, a different approach is taken in the use and manipulation of the elastomeric material as compared to the ""315 patent. In the later, the generator is for hydroelectric use, and the armature bars are permanently captured once they are installed. The elastomer wrapping/stretching technique utilized there will not work in other generators that require the windings to be lifted near their opposite ends during final winding closeup.
Accordingly, the present invention makes use of a temporary spacer placed on the radially inward side of the bar. A release line or wire is taped on the radially inward surface of the spacer, and the elastomer is then spirally wound completely about the bar, spacer and release line, along substantially the entire length of the bar (i.e., at least along that portion of the bar received in the radial slot).
After the bottom bar is located in the stator slot (or after all of the bottom bars are located in all of the respective radial slots), the release line is pulled to tear the elastomer longitudinally along the bar, freeing the elastomer to retract into and fill the slot spaces on either side of the bar. The spacer and release line are then removed and the assembly process continues via the addition of fillers, the second armature bar (for which the elastomer process described above is repeated), more fillers and finally the end wedges.
With this invention, the ends of bars can be lifted as necessary, before the release line is pulled, so that the elastomer will remain stretched during any such lifting.
Another feature of the invention relates to the sizing of the spacer in the height direction so that when released, the cut edges of the elastomer will retract to points just below the top edges of the bar to thereby eliminate or at least minimize trimming. In other words, the height of the spacer is selected as a function of the elasticity of the elastomer to maximize process efficiency.
Accordingly, in one aspect, the present invention relates to a generator armature bar support system comprising, in a temporary assembly state; an elongated armature bar having a bottom surface, a top surface, and a pair of side walls; a spacer temporarily located on the top surface of the armature bar; and an elastomer stretched and wound about the armature bar and spacer along substantially the length of the armature bar.
In another aspect, the invention relates to a method of a method of supporting a generator armature bar in a radial slot of a stator core body comprising:
a) locating a spacer on a radially inner surface of the armature bar;
b) wrapping the armature bar and spacer with an elastomer having shape memory properties along substantially the length of the armature bar, while stretching the elastomer to thereby reduce its thickness;
c) locating the armature bar in the radial slot of the stator core body such that the spacer is radially inward of the armature bar;
d) tearing the elastomer along a line adjacent a radially inner surface of the spacer to thereby cause the elastomer to relax and fill any air space between side walls of the radial slot and side walls of the armature bar; and
e) removing the spacer.